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Getting the saved set uid

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  Getting the saved set uid spud@potato.field - 2016-03-23 15:21 +0000
    Re: Getting the saved set uid Philip Guenther <guenther@gmail.com> - 2016-03-23 10:01 -0700
      Re: Getting the saved set uid spud@potato.field - 2016-03-24 09:40 +0000
        Re: Getting the saved set uid Philip Guenther <guenther@gmail.com> - 2016-03-24 09:10 -0700
          Re: Getting the saved set uid spud-u-dont-like@potato.field - 2016-03-25 12:50 +0000
            Re: Getting the saved set uid Barry Margolin <barmar@alum.mit.edu> - 2016-03-25 10:28 -0400
            Sarcasm in Usenet posts (Was: Getting the saved set uid) gazelle@shell.xmission.com (Kenny McCormack) - 2016-03-25 14:29 +0000
              Re: Sarcasm in Usenet posts (Was: Getting the saved set uid) Barry Margolin <barmar@alum.mit.edu> - 2016-03-25 11:49 -0400
                Re: Sarcasm in Usenet posts (Was: Getting the saved set uid) Ian Zimmerman <itz@buug.org> - 2016-03-26 09:41 -0700
              Re: Sarcasm in Usenet posts (Was: Getting the saved set uid) Philip Guenther <guenther@gmail.com> - 2016-03-25 10:10 -0700
        Re: Getting the saved set uid <william@wilbur.25thandClement.com> - 2016-03-24 13:16 -0700
          Re: Getting the saved set uid boon <fred900rbc@gmail.com> - 2016-04-01 04:42 -0700
            Re: Getting the saved set uid Noob <root@127.0.0.1> - 2016-04-01 19:16 +0200
              Re: Getting the saved set uid Barry Margolin <barmar@alum.mit.edu> - 2016-04-01 17:23 -0400
                Re: Getting the saved set uid boon <fred900rbc@gmail.com> - 2016-04-01 17:27 -0700
    Re: Getting the saved set uid boon <root@127.10.10.1> - 2016-03-24 12:08 +0100
      Re: Getting the saved set uid spud@potato.field - 2016-03-24 11:59 +0000
        Re: Getting the saved set uid boon <root@127.10.10.1> - 2016-03-24 13:19 +0100

#8209 — Getting the saved set uid

Is there a way in C of getting the current saved set user id (as set by
seteuid()) ?

--
Spud

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#8211

On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
> Is there a way in C of getting the current saved set user id (as set by
> seteuid()) ?

Does your system have useful manpages?  If so, "man -k" (also called "apropos") can be a quick start to these questions:

$ man -k saved
FvwmSaveDesk(1) - another FVWM desktop-layout saving module
gif2rgb(1) - convert images saved as GIF to 24-bit RGB triplets
getresgid, getresuid, setresgid, setresuid(2) - get or set real, effective and saved user or group ID
$ man getresuid
...
SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     int
     getresgid(gid_t *rgid, gid_t *egid, gid_t *sgid);

     int
     getresuid(uid_t *ruid, uid_t *euid, uid_t *suid);
...
     The getresgid() and getresuid() calls retrieve the real, effective, and
     saved group and user IDs of the current process, respectively.
...

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#8226

On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
Philip Guenther <guenther@gmail.com> wrote:
>On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
>> Is there a way in C of getting the current saved set user id (as set by
>> seteuid()) ?
>
>Does your system have useful manpages?  If so, "man -k" (also called
>"apropos") can be a quick start to these questions:

$ man getresgid
No manual entry for getresgid
$ man getresuid
No manual entry for getresuid

So, hows that sarcasm working out for you?

Turns out those functions are non standard. Supported on Linux and hp-ux
but thats about it. Not OS/X as you can see above.

Are there posix functions that do the same? And yes I have googled already
otherwise I wouldn't asking.

--
Spud

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#8233

On Thursday, March 24, 2016 at 2:40:45 AM UTC-7, sp...@potato.field wrote:
> On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
> Philip Guenther <guenther@gmail.com> wrote:
> >On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
> >> Is there a way in C of getting the current saved set user id (as set by
> >> seteuid()) ?
> >
> >Does your system have useful manpages?  If so, "man -k" (also called
> >"apropos") can be a quick start to these questions:
> 
> $ man getresgid
> No manual entry for getresgid
> $ man getresuid
> No manual entry for getresuid
> 
> So, hows that sarcasm working out for you?

No sarcasm intended: if you want to know what works on your system, then its own documentation is the place to start.

(If you're reacting to the word "useful", well, there have been many systems which completely lacked documentation, or where it was not installed by default, or was completely out of date; a caveat seemed necessary.)

 
> Turns out those functions are non standard. Supported on Linux and hp-ux
> but thats about it. Not OS/X as you can see above.
>
> Are there posix functions that do the same? And yes I have googled already
> otherwise I wouldn't asking.

Nope, there's nothing in POSIX for doing this.


Philip Guenther

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#8235

On Thu, 24 Mar 2016 09:10:36 -0700 (PDT)
Philip Guenther <guenther@gmail.com> wrote:
>On Thursday, March 24, 2016 at 2:40:45 AM UTC-7, sp...@potato.field wrote:
>> On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
>> Philip Guenther <guenther@gmail.com> wrote:
>> >On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
>> >> Is there a way in C of getting the current saved set user id (as set by
>> >> seteuid()) ?
>> >
>> >Does your system have useful manpages?  If so, "man -k" (also called
>> >"apropos") can be a quick start to these questions:
>> 
>> $ man getresgid
>> No manual entry for getresgid
>> $ man getresuid
>> No manual entry for getresuid
>> 
>> So, hows that sarcasm working out for you?
>
>No sarcasm intended: if you want to know what works on your system, then its
>own documentation is the place to start.

No shit. Obviously it didn't occur to you that someone posting to a usenet 
unix group asking about some obscure low level system functionality has 
probably heard of man pages and already tried them.

--
Spud

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#8236

In article <BuaJy.88011$bx.57078@fx35.am4>,
 spud-u-dont-like@potato.field wrote:

> On Thu, 24 Mar 2016 09:10:36 -0700 (PDT)
> Philip Guenther <guenther@gmail.com> wrote:
> >On Thursday, March 24, 2016 at 2:40:45 AM UTC-7, sp...@potato.field wrote:
> >> On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
> >> Philip Guenther <guenther@gmail.com> wrote:
> >> >On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field 
> >> >wrote:
> >> >> Is there a way in C of getting the current saved set user id (as set by
> >> >> seteuid()) ?
> >> >
> >> >Does your system have useful manpages?  If so, "man -k" (also called
> >> >"apropos") can be a quick start to these questions:
> >> 
> >> $ man getresgid
> >> No manual entry for getresgid
> >> $ man getresuid
> >> No manual entry for getresuid
> >> 
> >> So, hows that sarcasm working out for you?
> >
> >No sarcasm intended: if you want to know what works on your system, then its
> >own documentation is the place to start.
> 
> No shit. Obviously it didn't occur to you that someone posting to a usenet 
> unix group asking about some obscure low level system functionality has 
> probably heard of man pages and already tried them.

The problem with the infamous "RTFM" recommendation is that you have to 
know which FM to R. And if you knew that, you wouldn't be asking how to 
do what you want. The Unix man pages aren't really designed well for 
learning from, they're mostly useful as references for the details (what 
are the command options, what order are the function arguments, etc.).

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

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#8237 — Sarcasm in Usenet posts (Was: Getting the saved set uid)

In article <BuaJy.88011$bx.57078@fx35.am4>,
 <spud-u-dont-like@potato.field> wrote:
...
>>> So, hows that sarcasm working out for you?
>>
>>No sarcasm intended: if you want to know what works on your system, then its
>>own documentation is the place to start.
>
>No shit. Obviously it didn't occur to you that someone posting to a usenet 
>unix group asking about some obscure low level system functionality has 
>probably heard of man pages and already tried them.

Yeah, I'm with you, spud.

To be fair, it is just about (but not quite) possible to read the other
posters post and not feel like you're being slimed.  If you really bend
over backwards and give him every benefit of the doubt, yes, it is possible
it was intended as "straight".

But, given the usual Usenet culture, that's all straining credulity.

And, yes, it is also an integral part of the Usenet culture to:

    a) Assume that the posters you're preaching to are total morons (an
	assumption which is, sad to say, usually valid - but not always)

    b) Assume that the posters you're preaching to don't know about the
	basic stuff - like man pages and so on.  Again, this assumption is
	usually, but not always, valid.

-- 
"The God of the Old Testament is arguably the most unpleasant character
in all fiction: jealous and proud of it; a petty, unjust, unforgiving
control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic,
homophobic, racist, infanticidal, genocidal, filicidal, pestilential,
megalomaniacal, sadomasochistic, capriciously malevolent bully."

 - Richard Dawkins, The God Delusion -

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#8238 — Re: Sarcasm in Usenet posts (Was: Getting the saved set uid)

In article <nd3i0u$53q$3@news.xmission.com>,
 gazelle@shell.xmission.com (Kenny McCormack) wrote:

> In article <BuaJy.88011$bx.57078@fx35.am4>,
>  <spud-u-dont-like@potato.field> wrote:
> ...
> >>> So, hows that sarcasm working out for you?
> >>
> >>No sarcasm intended: if you want to know what works on your system, then its
> >>own documentation is the place to start.
> >
> >No shit. Obviously it didn't occur to you that someone posting to a usenet 
> >unix group asking about some obscure low level system functionality has 
> >probably heard of man pages and already tried them.
> 
> Yeah, I'm with you, spud.
> 
> To be fair, it is just about (but not quite) possible to read the other
> posters post and not feel like you're being slimed.  If you really bend
> over backwards and give him every benefit of the doubt, yes, it is possible
> it was intended as "straight".
> 
> But, given the usual Usenet culture, that's all straining credulity.
> 
> And, yes, it is also an integral part of the Usenet culture to:
> 
>     a) Assume that the posters you're preaching to are total morons (an
> 	assumption which is, sad to say, usually valid - but not always)
> 
>     b) Assume that the posters you're preaching to don't know about the
> 	basic stuff - like man pages and so on.  Again, this assumption is
> 	usually, but not always, valid.

If it's not sarcasm, it's passive-aggressiveness. Either way, it's 
condescending and annoying.

I'm embarassed to admit that sometimes I succumb to the temptation on 
StackOverflow, asking things like "Is Google broken for you?" Usually 
this is when I simply plug their error message into the search engine 
and it takes me immediately to another SO question that's directly on 
point.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

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#8246 — Re: Sarcasm in Usenet posts (Was: Getting the saved set uid)

On 2016-03-25 11:49 -0400, Barry Margolin wrote:

> I'm embarassed to admit that sometimes I succumb to the temptation on 
> StackOverflow, asking things like "Is Google broken for you?" Usually 
> this is when I simply plug their error message into the search engine 
> and it takes me immediately to another SO question that's directly on 
> point.

If Google got big before the questing person was 40, you've the "dog
old, trick new" problem.  I still find myself starting to compose Usenet
or Stack Overflow questions and only stopping right before I push the
commit button/hit the Enter key, suddenly remembering search engines
exist.  More impulsive natures may not remember until it's too late.

-- 
Please *no* private copies of mailing list or newsgroup messages.
Rule 420: All persons more than eight miles high to leave the court.

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#8239 — Re: Sarcasm in Usenet posts (Was: Getting the saved set uid)

On Friday, March 25, 2016 at 7:29:53 AM UTC-7, Kenny McCormack wrote:
> In article <BuaJy.88011$bx.57078@fx35.am4>,
>  <spud-u-dont-like@potato.field> wrote:
> ...
> >>> So, hows that sarcasm working out for you?
> >>
> >>No sarcasm intended: if you want to know what works on your system, then its
> >>own documentation is the place to start.
> >
> >No shit. Obviously it didn't occur to you that someone posting to a usenet 
> >unix group asking about some obscure low level system functionality has 
> >probably heard of man pages and already tried them.

Spud, my apologies to you for phrasing my response in a condescending way.


I feel this thread would have been many messages shorter if the clarification in your second post (that you were interested in methods that were POSIX compliant and/or usable on OSX) had been mentioned earlier.  That doesn't excuse the tone of my response though.


...
> And, yes, it is also an integral part of the Usenet culture to:
> 
>     a) Assume that the posters you're preaching to are total morons (an
> 	assumption which is, sad to say, usually valid - but not always)
> 
>     b) Assume that the posters you're preaching to don't know about the
> 	basic stuff - like man pages and so on.  Again, this assumption is
> 	usually, but not always, valid.

c) take more interest in the meta discussion about *how* questions were asked and answered then in discussing the actual question and answer.  As you recently said  in another thread, Kenny:

# You just gotta love this thread.  Usenet at its finest. 
# 
# 30+ responses and not one single post having anything to do with the BASIC 
# language (which is what this thread is supposed to be about). 

Of course, my original reply was only 5% "here's the answer" and 95% "here's how you might have gotten the answer".  Oh well.



Philip Guenther

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#8234

spud@potato.field wrote:
> On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
> Philip Guenther <guenther@gmail.com> wrote:
>>On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
>>> Is there a way in C of getting the current saved set user id (as set by
>>> seteuid()) ?
>>
>>Does your system have useful manpages?  If so, "man -k" (also called
>>"apropos") can be a quick start to these questions:
> 
> $ man getresgid
> No manual entry for getresgid
> $ man getresuid
> No manual entry for getresuid
> 
> So, hows that sarcasm working out for you?
> 
> Turns out those functions are non standard. Supported on Linux and hp-ux
> but thats about it. Not OS/X as you can see above.
> 
> Are there posix functions that do the same? And yes I have googled already
> otherwise I wouldn't asking.

You can download the POSIX specification for free from

        https://www2.opengroup.org/ogsys/catalog/c138

or just visit it online at

        http://pubs.opengroup.org/onlinepubs/9699919799/

The index of system interfaces is incomparably useful. Select "System
Interfaces" from the top-left frame, then "System Interfaces" in the
bottom-left frame. That gives you the full list of system interfaces (aka
syscalls and libc routines), and AFAICT there's nothing like getreuid
available.

The history and rationale sections of related interface definitions often
provide useful information. As do other chapters in the Base Definitions and
System Interfaces volumes. For example, section 3.331 Saved Set-User-ID
directs you to the setuid and exec-family definitions for more information,
and indeed the rationale section of setuid contains much information about
the semantics of uids.

If you're serious about C or Unix programming it would be prudent to have
local copies of the POSIX and C standards.[1] Once you become familiar with
them I think you'll find them much more convenient and reliable in general
than either man pages (especially the inconsistent Linux man pages),
Googling, or technical forums. Only once I know or suspect I'm dealing with
vendor extensions do I bother with anything else, and by then the standards
have framed things such that I'm much more productive when searching and
analyzing other sources.


[1] The draft C99 and C11 standards are freely available, and but for
inconsequential typos identical to the published standards. See

        http://www.open-std.org/jtc1/sc22/wg14/www/standards

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#8291

On Thursday, March 24, 2016 at 9:30:07 PM UTC+1, wil...@wilbur.25thandclement.com wrote:
> spud@potato.field wrote:
> > On Wed, 23 Mar 2016 10:01:14 -0700 (PDT)
> > Philip Guenther <guenther@gmail.com> wrote:
> >>On Wednesday, March 23, 2016 at 8:21:55 AM UTC-7, sp...@potato.field wrote:
> >>> Is there a way in C of getting the current saved set user id (as set by
> >>> seteuid()) ?
> >>
> >>Does your system have useful manpages?  If so, "man -k" (also called
> >>"apropos") can be a quick start to these questions:
> > 
> > $ man getresgid
> > No manual entry for getresgid
> > $ man getresuid
> > No manual entry for getresuid
> > 
> > So, hows that sarcasm working out for you?
> > 
> > Turns out those functions are non standard. Supported on Linux and hp-ux
> > but thats about it. Not OS/X as you can see above.
> > 
> > Are there posix functions that do the same? And yes I have googled already
> > otherwise I wouldn't asking.
> 
> You can download the POSIX specification for free from
> 
>         https://www2.opengroup.org/ogsys/catalog/c138
> 
> or just visit it online at
> 
>         http://pubs.opengroup.org/onlinepubs/9699919799/
> 
> The index of system interfaces is incomparably useful. Select "System
> Interfaces" from the top-left frame, then "System Interfaces" in the
> bottom-left frame. That gives you the full list of system interfaces (aka
> syscalls and libc routines), and AFAICT there's nothing like getreuid
> available.
> 
> The history and rationale sections of related interface definitions often
> provide useful information. As do other chapters in the Base Definitions and
> System Interfaces volumes. For example, section 3.331 Saved Set-User-ID
> directs you to the setuid and exec-family definitions for more information,
> and indeed the rationale section of setuid contains much information about
> the semantics of uids.
> 
> If you're serious about C or Unix programming it would be prudent to have
> local copies of the POSIX and C standards.[1] Once you become familiar with
> them I think you'll find them much more convenient and reliable in general
> than either man pages (especially the inconsistent Linux man pages),
> Googling, or technical forums. Only once I know or suspect I'm dealing with
> vendor extensions do I bother with anything else, and by then the standards
> have framed things such that I'm much more productive when searching and
> analyzing other sources.
> 
> 
> [1] The draft C99 and C11 standards are freely available, and but for
> inconsequential typos identical to the published standards. See
> 
>         http://www.open-std.org/jtc1/sc22/wg14/www/standards

According to my manual page, sendto() conforms to POSIX.1-2001. Is this normal?

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#8300

On 01/04/2016 13:42, boon wrote:

> According to my manual page, sendto() conforms to POSIX.1-2001. Is this normal?

Are you posting to the wrong thread by any chance?

This is the latest man page:
http://man7.org/linux/man-pages/man2/send.2.html

This is the latest spec:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/sendto.html

Regards

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#8303

In article <ndma7f$nur$1@dont-email.me>, Noob <root@127.0.0.1> wrote:

> On 01/04/2016 13:42, boon wrote:
> 
> > According to my manual page, sendto() conforms to POSIX.1-2001. Is this 
> > normal?
> 
> Are you posting to the wrong thread by any chance?

I was wondering the same thing -- it seems like this is more related to 
the "unix socket exercise" thread.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

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#8304

Yes. I posted to the wrong thread. I apologize.

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#8227

On 03/23/2016 04:21 PM, spud@potato.field wrote:
> Is there a way in C of getting the current saved set user id (as set by
> seteuid()) ?

why not calling geteuid() to save the effective uid before calling 
seteuid()?

> --
> Spud
>


--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

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#8230

On Thu, 24 Mar 2016 12:08:03 +0100
boon <root@127.10.10.1> wrote:
>On 03/23/2016 04:21 PM, spud@potato.field wrote:
>> Is there a way in C of getting the current saved set user id (as set by
>> seteuid()) ?
>
>why not calling geteuid() to save the effective uid before calling 
>seteuid()?

I was asking more out of curiousity than for any practical reason since, yes,
you could just save the original one yourself. Though it might be potentially 
useful for a child process if its parent calls seteuid() then does a fork-exec
though I don't know if the saved set uid would be passed to the child in this 
case.

--
Spud

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#8232

On 03/24/2016 12:59 PM, spud@potato.field wrote:
> On Thu, 24 Mar 2016 12:08:03 +0100
> boon <root@127.10.10.1> wrote:
>> On 03/23/2016 04:21 PM, spud@potato.field wrote:
>>> Is there a way in C of getting the current saved set user id (as set by
>>> seteuid()) ?
>>
>> why not calling geteuid() to save the effective uid before calling
>> seteuid()?
>
> I was asking more out of curiousity than for any practical reason since, yes,
> you could just save the original one yourself. Though it might be potentially
> useful for a child process if its parent calls seteuid() then does a fork-exec
> though I don't know if the saved set uid would be passed to the child in this
> case.


AFAIK, the parent have not to call seteuid() to drop some privileges. 
This has to be done by the child process.

On Linux:

man credentials (7)

A child process created by fork(2) inherits copies of its parent's user 
and groups IDs.   During  an  execve(2),  a  process's  real user and 
group ID and supplementary group IDs are preserved; the effective and 
saved set IDs may be changed, as described in execve(2).

man execve (2)

  If  the  set-user-ID bit is set on the program file pointed to by 
filename, and the underlying filesystem is not mounted nosuid (the 
MS_NOSUID flag for mount(2)), and the calling process is not being 
ptraced, then the effective user ID of the calling process is changed to 
that of the owner of the program file.  Similarly, when the set-group-ID 
bit of the program  file  is  set the effective group ID of the calling 
process is set to the group of the program file.

The effective user ID of the process is copied to the saved set-user-ID; 
similarly, the effective group ID is copied to the saved set-group-ID. 
This copying takes place after any  effective ID changes that occur 
because of the set-user-ID and set-group-ID permission bits.



> --
> Spud
>


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